Abu al-Tayyib Sanad ibn Ali al-Yahudi (died c. 864 C.E.), was a ninth-century Iraqi Jewish astronomer, translator, mathematician and engineer employed at the court of the Abbasid caliph Al-Ma'mun. A later convert to Islam, Sanad's father was a learned Jewish astronomer who lived and worked in Baghdad. Biography He is known to have translated and modified the Zij al-Sindhind. The Zij al-Sindhind was the first astronomical table ever introduced in the Muslim World. As a mathematician Sanad ibn ʿAlī was a colleague of al-Khwarizmi and worked closely with Yaqūb ibn Tāriq together they calculated the diameter of the Earth and other astronomical bodies. He also wrote a commentary on Kitāb al-ğabr wa-l-muqābala and helped prove the works of al-Khwarizmi. The decimal point notation to the Arabic numerals was introduced by Sanad ibn Ali. According to Ibn Abi Usaibia: the Banū Mūsā brothers out of sheer professional jealousy kept him away from Abbasid Caliph al-Mutawakkil at his new capital Samarra and had caused Sanad ibn ʿAlī to be sent away to Baghdad. Both Ja'far Muhammad ibn Mūsā ibn Shākir and Ahmad ibn Mūsā ibn Shākir delegated the work of digging a great canal instead to Al-Farghani and thus ignoring Sanad ibn ʿAlī, the better engineer. Al-Farghani committed a great error, making the beginning of the canal deeper than the rest and water never reached the new garrison of Al-Ja'fariya. News of this greatly angered al-Mutawakkil and the two Banū Mūsā brothers were saved from severe punishment only by the gracious willingness of Sanad ibn ʿAlī, to vouch the corrections of Al-Farghani's calculations thus risking his own welfare and possibly his life. References Astronomers from the Abbasid Caliphate Astronomers of the medieval Islamic world Mathematicians from the Abbasid Caliphate Medieval engineers Year of death unknown 9th-century people from the Abbasid Caliphate Year of birth unknown 9th-century translators Converts to Islam from Judaism 9th-century Jews Jews from the Abbasid Caliphate